Question

Roller Skating Momentum

Two roller skaters are skating on a straight roller skating track and practicing the skills they need to play roller derby. Roller Skater 1 is behind Roller Skater 2. Roller Skater 1 pushes Roller Skater 2 from behind to help Roller Skater 2 gain velocity, as shown in the picture. 



A student took data on the roller skaters in an attempt to support the claim, "the total momentum of a system of objects is conserved when there is no net force on the system." The table shows the data.

Roller SkaterMass (kg)Velocity Before Push (m/s)Velocity After Push (m/s)155.04.002.50250.03.495.14

Multiple Choice Question

What is the initial momentum of Roller Skater 2?

A. 

138 kg·m/s

B. 

175 kg·m/s

C. 

220 kg·m/s

D. 

257 kg·m/s

Answer 1

Initial momentum p = m v. For Roller Skater 2: p = 50.0 kg × 3.49 m/s = 174.5 kg·m/s ≈ 175 kg·m/s. Answer: B.